An electrochemical measuring cell of his type has become known from DE 41 36 779 A1. Individual working electrodes in the form of spatially separated measuring fields are arranged on a surface of an electrolyte for the simultaneous detection of different gas components, while the common counterelectrode and the common reference electrode are arranged on the opposite side of the electrolyte. The electrodes are connected to a potentiostatic evaluating circuit, which contains individual control circuits, with which the potentials of the working electrodes relative to the reference electrode can be maintained at constant values individually and independently from one another.
Besides the analysis of toxic or combustible gases, the determination of the percentage of oxygen in the ambient atmosphere is also necessary in numerous measurement and monitoring tasks in the protection of people and at the workplace. Sensors for oxygen are based either on the galvanometric or the potentiometric principle of measurement, with the oxidation of a lead or silver anode. The maximum service life of such cells depends on the amount of anode material that can be reacted and the percentage of oxygen in the atmosphere to be monitored. The typical service life of such oxygen measuring cell is about up to 2 years.
Sensors for the analysis of toxic or combustible gases are frequently based on the amperometric principle of measurement, and their service life is usually longer than 2 years. The measuring cells must therefore be replaced at different times in measuring devices that are equipped with one measuring cell for O.sub.2 measurement and another measuring cell for monitoring harmful gases.
An amperometric sensor for the measurement of the percentage of oxygen in the air, in which the reference electrode consists of a sintered mixture of metal and its metal oxide, as a result of which a long service life of the reference electrode and consequently of the entire sensor is obtained, has been known from DE 42 31 256. However, the prior-art gas sensor is suitable for the detection of one component only.